The present work concerns on the investigation of the role of polyethylene glycols (PEGs) as masking agent for amelioration of extraction-separation of La(III), Eu(III) and Er(III) ions by the acidic extractant bis(2-ethylhexyl)phosphoric acid (DEHPA). The studied solvent extraction system is based on the combination of chelating effect of DEHPA in the organic phase on the one hand, and the binding properties of the PEGs in the aqueous phase, on the other hand, to provide an improvement in separation of La(III), Eu(III) and Er(III) ions. The first part of this study deals with effect of diluent used as organic solvent on the separation efficiency of bis(2-ethylhexyl)phosphoric acid towards lanthanum, europium and erbium ions. Then, the influence of the presence of three polyethylene glycols, with molecular weights 200, 400 and 2000 (PEG200, PEG400 and PEG2000), in the aqueous phase on the separation of the studied metal ions was evaluated and discussed.